Connecting coax cable to GPIO pins for SPDIF_OUT?

Hi All,

I am at the point in my project where I need to connect a coax cable from the SPDIF_OUT pins on the GPIO outputs on my VIM3 and I need guidance on the correct method. Am I correct

that I should solder a single pin to the centre connector and a single pin to the outer shield then attach the centre connector pin to GPIO pin 13 and the outer shield pin to GPIO pin 14 and run the coax cable out to the SPDIF input on my DSP.

Does this sound correct?

Thanks for any replies.

Should work, I have never used coax for it, as I connect to a board, but it should be fine. Pin 13 is signal, pin 14 is ground.
Try to reduce strain on the GPIO pins.

Use transformator i use murato 101 to spdif conections.
It save gpio …

Thanks guys.

“Use transformator i use murato 101 to spdif conections.
It save gpio …”
Do you mean it saves the GPIO from mechanical strain or some kind of electrical strain?
Also can I use the GPIO SPDIF out without using a transformer?

Electrical damage can burn cpu, if your dont use galvanic transformer.

I have connected directly to the GPIO. Have not had any issues so far. I am in favor of protection, but I guess it can be as simple or as complex as one desires.
I have also used the GPIO pins to drive an optical output.

Thank you both for all the info. I have ordered two of the Murata DA101C from Mouser as I would rather be safe than sorry.

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Its unlikely that the GPIO is strong enough to drive the coax without a buffer transistor amplifier. Likely result is damage to board or inconsistent signal.


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Now this puts a different light on things. By any chance do you have a link to a buffer transistor amplifier that would work with the VIM3?

This is a good place to consider the options

I use a cheap little USB to SPIDF converter I got from China.


Thanks for the info and link Shoog. I’m going to try this circuit as it looks simple and easy to implement. I welcome input from anyone who has opinions on this.

                                                     S/PDIF output
                                                      (RCA or BNC)

TTL level signal ----- -----| O-----680R-- --------- ------- center pin
| |/ | | |
| | )||(
| |\ | )||(
-----| O-----680R-- )||(
|/ | )||(
100R | |
74HC04 | | ------- ground
---- ---- T1

Hi @Donanon any luck with the TTL SPDIF to Coax circuit? I hope it worked just fine. Can we pick any of the schematic or is it a specific one. It would be wonderful if you could publish a DIY guide along with the component list for us noobs.
Thank you!

Sorry about the late reply. I gave up on connecting directly to the VIM3 and bought a ToneBoard which has S/PDIF output which I will use to connect directly to my DSP. A lot less mucking about and I have always been a fan of plug and play.

Be warned that the software support for this may be absent from most OS’s for the VIM’s. The SPIDF out feature is not supported in Coreelec.


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Thanks @Donanon! I shall build one such buffer and update.

@shoog I will be using it with volumio. So just hoping that it might support spdif from gpio.
Is the gpio spdif a TTL or a CMOS level signal? Tia.

Dont know if its TTL or CMOS. The issue is that there is a software switch to enable the spidf passthrough and most systems don’t set it correctly.
A simple LED socket should work straight off the gpio pin, but for coax its better to include a buffer transistor or their is a potential to draw to much current from the gpio.


@shoog technically, its better to add a buffer transistor to any electrical component not just the coax, if you are using a single component then a buffer transistor setup is too much rather use a simple resistor to limit current

If it is something else like a i2C LCD etc. its ok to use the pins directly without buffer.

The LED Toslink socket is a predictable fixed load which will not draw to much current so is safe to attach straight to the pin.
Its generally better to buffer but this adds a level of complexity which the toslink avoids.